What Is an Autonomous System (AS)?

Overview of AS

An autonomous system (AS) is a collection of IP address prefixes managed by a single organization or entity that follows a unified routing policy. Each AS is assigned a unique identifier called an autonomous system number (ASN) by one of the five Regional Internet Registries (RIRs): AFRINIC, APNIC, ARIN, LACNIC, or the RIPE NCC.

Why AS Information Is Important

Autonomous systems define how data moves across the internet. For cybersecurity teams, ASN identification is crucial for detecting malicious activity, such as botnets or suspicious traffic originating from known bad actors. Businesses and ISPs rely on ASN analysis to optimize network performance, reduce latency, and improve load balancing by better understanding routing paths.

How to Lookup an AS Using IPinfo

With IPinfo’s ASN API or database download, users can look up AS details, including organization names, countries, and related IP prefixes. This information helps identify which AS an IP address belongs to, offering a view into network trends and potential security risks. For businesses concerned with fraud prevention, IPinfo’s AS data can be used to flag suspicious IP addresses, helping reduce exposure to malicious actors and improve overall cybersecurity posture.

Links to Related Documentation and Tooling

• ASN API Developer Resource
• IP to ASN Database Developer Resource
• IP API Responses Developer Resource

Additional Resources

• Community Post: ASN Explained
• Blog: IPinfo's Journey to Accurate IP Data